1. Field of the Invention
The present invention relates to methods, treatment compositions and treatment systems for forming essentially transparent, detachable and renewable protective coatings on a receptive surface by a process of applying to the receptive surface a treatment composition comprising a plurality of hydrophobic particles colloidally dispersed in a volatile solvent; allowing the volatile solvent to evaporate; and thereby depositing a coating on the receptive surface that provides dirt- and water-repellent properties, self-cleaning and easier next time cleaning benefits.
2. Description of the Related Art
The principle of self-cleaning coatings is wellknown in the literature. The effect generally requires two essential features: one being a hydrophobic surface or hydrophobic coating on a surface; and the second being some degree of surface roughness which combine to produce a structured “superhydrophobic” surface, exhibiting high water contact angles that act to readily repel water and shed adherent particulate soils with even small amounts of water alone, without requiring the use of typical cleaning agents.
The use of hydrophobic materials, such as perfluorinated polymers, to produce hydrophobic surfaces is known. A further development of these surfaces consists in structuring the surfaces in the μm to nm range. U.S. Pat. No. 5,599,489 discloses a process in which a surface can be rendered particularly repellent by bombardment with particles of appropriate size, followed by perfluorination.
A suitable combination of structure and hydrophobic properties permits even small amounts of water moving on the surface to entrain adherent dirt particles and clean the surface (see, for example, U.S. Pat. No. 6,660,363; U.S. Pat. No. 3,354,022).
The prior art of EP-B-0 933 388 requires an aspect ratio>1 and a surface energy of less than 20 mN/m for these self-cleaning surfaces; the aspect ratio being defined here as the quotient which is the ratio of the height of the structure to its width. The abovementioned criteria are typically found in nature, for example, in the lotus leaf. The surface of the plant is composed of a hydrophobic waxy material and has elevations separated by a few μm. Water droplets substantially contact only the peaks of the elevations. There are many descriptions in the literature of water-repellent surfaces of this type.
EP-A-0 909 747 teaches a process for generating a self-cleaning surface. The surface has hydrophobic elevations whose height is from 5 to 200 μm. A surface of this type is produced by applying a dispersion of pulverulent particles and of an inert material in a siloxane solution and then curing. The structure-forming particles are therefore secured to the surface by way of an auxiliary medium.
U.S. Pat. Pub. No. 2005/0136217A1 concludes that it is technically possible to render the surfaces of articles artificially self-cleaning. The surface structures necessary for this purpose, which are composed of elevations and depressions, have a separation in the range from 0.1 to 200 μm between the elevations of the surface structures, and have an elevation height in the range from 0.1 to 100 μm. The materials used for this purpose are composed of hydrophobic polymers or of lastingly hydrophobized material. Release of the particles from the carrier matrix has to be prevented.
This principle has been borrowed from nature. Small contact surfaces lower the level of van der Waals interaction responsible for adhesion to flat surfaces with low surface energy. For example, the leaves of the lotus plant have elevations composed of a wax, and these reduce the area of contact with water.
Processes for producing these structured surfaces are likewise known. Besides the use of a master template to mold these structures in fill-in detail by an injection molding or embossing processes, there are also known processes that utilize the application of particles to a surface. This is disclosed, for example, in U.S. Pat. No. 5,599,489.
Recently, attempts have been made to provide self-cleaning surfaces on textiles. It has been found that self-cleaning surfaces can be generated by applying fine-particle SiO2 (AEROSIL®) to textiles. In this process, the AEROSIL® materials are bonded into the polymer matrix of the textile fiber, using a solvent that partially dissolves the fiber to effect adhesion
U.S. Pat. Pub. No. 2004/0154106A1 describes polymer fibers with self-cleaning surfaces. In the prior art disclosure, the self-cleaning surface is obtained by exposure to a solvent, which comprises structure-forming particles, using the solvent to solvate the surface of the polymer fibers, adhesion of the structure-forming particles to the solvated surface, and removing the solvent. The disadvantage of this process is that, during processing of the polymer fibers (spinning, knitting, etc.), the structure-forming particles, and therefore the structure that renders the surface self-cleaning, can become damaged or sometimes lost entirely, the result being that the self-cleaning effect is also lost.
U.S. Pat. Pub. No. 2005/0103457A1 describes textile sheets with a self-cleaning and water-repellent surface composed of at least one synthetic and/or natural textile base material A, and of an artificial, at least to some extent, hydrophobic surface with elevations and depressions composed of particles that have been securely bonded to the base material A without adhesives, resins, or coatings. The hydrophobic surfaces are obtained by treating the base material A with at least one solvent that comprises the undissolved particles, and removing the solvent, whereupon at least some of the particles become securely bonded to the surface of the base material A. However, the disadvantage of this prior art process is the very complicated finishing of the textile surfaces. Moreover, this prior art process requires precise matching of the solvent to the base material of the textiles. However, in clothing there are generally mixed fabrics present, and this matching therefore becomes more complicated. If the matching of the solvents is not precise, the result can be irreparable damage to parts of the clothing. The textile surfaces therefore have to be treated prior to tailoring.
U.S. Pat. No. 6,800,354 describes substrates with a self-cleaning surface and a process for a permanent coating of the substrates providing the self-cleaning properties. The process includes the following steps: (1) coating of the surface with a composition containing structure forming particles and a layer forming material; (2) forming a cohesive layer that fixes the structure forming particles firmly to the surface, and then; (3) hydrophobizing the structured surface with a hydrophobizing agent which adheres firmly to the structured surface. The structure forming particles preferably have an average diameter of less than 100 nm, more preferably in the range between 5 and 50 nm. In an example, a float glass with a transparent self-cleaning surface was produced by coating the glass with a composition by means of a screen printing process using a 100 T screen. The composition included 0.5 wt. % boric acid and 4 wt. % pyrogenic silica with an average diameter of the primary particles of 12 nm in a water friendly medium. After drying, the coating was shock fired at 660° C. for a duration of 4 min. The hydrophobization of the structured stoved surface was carried out by introducing an ethanolic solution of tridecafluorooctyltriethoxysilane over the surface and curing at an elevated temperature. The disadvantages of the described method is its multiple-step nature and the requirement of a high temperature process. In addition, it results in a permanent coating, which cannot be easily detached by a simple cleaning procedure.
All of these coatings are characterized in that they are intended to be applied permanently to the articles, and thus have the disadvantage that they cannot be simply removed and reapplied in the event of impairment by scratching, discoloration or any other damage to the coating, surface or coated surface structure. If this type of damage occurs, the article either has to be freed from the surface structure by a complicated method and retreated, or has to be disposed of if its appearance is no longer acceptable.
U.S. Pat. Pub. No. 2005/0136217A1 describes a process for producing detachable coatings with dirt- and water-repellent properties. These coatings of the prior art are produced by spray-application of hydrophobic alcohols, such as nonacosan-10-ol, or of alkanediols, such as nonacosane-5,10-diol, or of waxes. The coatings of U.S. Pat. Pub. No. 2005/0136217A1 can be removed from articles by strong mechanical forces, e.g. scratching, brushing, or high-pressure water treatment, or by treatment with water which comprises detergents that disperse some of the structure-formers. A disadvantage of the prior art coatings disclosed in U.S. Pat. Pub. No. 2005/0136217A1 is the strong forces needed for mechanical removal of the coating. The use of strong forces for the mechanical removal of the coating runs the risk that when the coating is removed the surface of the article itself will also be damaged. Treatment with water that comprises detergents can likewise lead to damage to the article, depending on its nature.
U.S. Pat. Pub. No. 2004/0213904 describes a process for producing detachable dirt- and water-repellent surface coatings on articles, wherein during the coating process, hydrophobic particles are applied to the surface of the articles, thus generating a structure with elevations on the surface of the articles that has dirt- and water-repellent properties, which comprises suspending the hydrophobic particles in a solution of an alkyl-modified silicone wax in a highly volatile siloxane, applying this suspension to at least one surface of an article, and then removing the highly volatile siloxane. In this document examples of compositions for producing those surface coatings are given and procedures how they are made. The compositions are dispersions of fumed silica particles present at 1 to 2 wt. % of the total weight of the dispersion in a solution of an alkyl-modified silicone wax present at 0.5 wt. % in decamethylcyclopentasiloxane. They are produced by dissolving the alkyl-modified silicone wax in decamethylcyclopentasiloxane and then dispersing the fumed silica in this solution with vigorous stirring. Although the therein described process for producing detachable dirt- and water-repellent surface coatings proved to provide better results with respect to run-off behavior of water droplets and gloss values on various surfaces compared to processes known from the prior state of the art, it still has some disadvantages. Especially on high gloss surfaces such as glass, brushed metal and varnished or painted surfaces the coating is easily perceptible as a grayish or hazy layer by the naked eye which is not acceptable for many applications.
The various approaches employed in the prior art are directed to modification of the targeted surfaces to have sufficient roughness to provide a coating capable of exhibiting the Lotus effect, and generally produce non-transparent coatings and films that suffer from poor visual appearance, particularly on glossy, shiny and/or highly reflective surfaces. Further, approaches that provide protective coatings with improved visual appearances rely on fixatives to firmly attach and/or embed materials onto the treated surface, accompanied by chemical, physical and/or thermal processes required to produce them and resulting in permanent and non-renewable treated articles.
It is therefore an object of the present invention to provide a method, treatment compositions and treatment systems which can produce essentially transparent protective surface coatings on a wide variety of materials and form treated articles providing dirt- and water-repellency and related surface protective benefits.
It is therefore an object of the present invention to provide a method, treatment compositions and treatment systems which can produce detachable and renewable dirt- and water-repellent surface coatings on a receptive surface, and which can also treat articles to give a relatively durable coating, which, however, can be detached using simple means, without requiring any chemical or physical modification or change to the underlying substrate, which may then be readily restored to its pristine initial state when desired.
It is a further object of the present invention to provide a method, treatment compositions and treatment systems which can provide receptive surfaces and treated articles with transparent, detachable and renewable protective surface coatings formable on a wide variety of materials and substrates.
It is a further object of the present invention to provide a method, treatment compositions and treatment systems which can provide receptive surfaces with transparent, detachable and renewable protective surface coatings, which can be easily renewed by removing the coatings by simple means and reapplying the coatings, on a wide variety of materials and substrates.
It is yet a further object of the present invention to provide a method, treatment compositions and treatment systems which can provide receptive surfaces with transparent, detachable and renewable protective surface coatings on a wide variety of materials which thereby exhibit dirt- and water-repellency, self-cleaning and easier next time cleaning benefits.
It is yet another object of the present invention to provide a treatment system for applying and forming a protective coating on a receptive surface using an applicator for applying a treatment composition for forming an essentially transparent, detachable and renewable protective coating on a receptive surface.